This invention relates to a laminate type heat exchanger, and more particularly to a laminate type heat exchanger for use as an evaporator of an automotive air conditioning system or the like.
A conventional laminate type heat exchanger of this type comprises a plurality of tubular elements each formed of a pair of generally flat stamped plates joined together in an abutting manner along angled outer peripheral edges thereof, the tubular elements each having tanks at one end thereof, a plurality of fins, typically corrugated, the tubular elements and the fins being superposed one upon another in an alternate manner to form a laminate structure, and a pair of end plates attached to outermost ones of the tubular elements at opposite ends of the laminate structure, as disclosed in Japanese Provisional Patent Publication (Kokai) No. 63-153397.
This laminate type heat exchanger has a tank section at one end thereof, and each end plate and its associated stamped plate are joined together at one end of the tubular element remote from the tank section in a manner as shown in FIG. 1. As shown in the figure, the outermost stamped plate 100 has an inner side surface thereof formed with a generally flat refrigerant passage-forming recess 102 bordered by its angled outer peripheral edge 101. A multiplicity of projections or beads 103 are formed integrally over the surface of the refrigerant passage-forming recess 102. The end plate 110 which is attached to each outermost stamped plate 100 is so shaped or stamped as to have a joining peripheral portion (joining portion) 111 abutting against an outer side surface 102a of the stamped plate 100 at a location corresponding to at least two recessed portions of the recess 102, and a swelled main portion 112 defining therein a space accommodating a corrugated fin 120 together with the outer side surface 102a of the stamped plate 100. The joining portion 111 of the end plate 110 is brazed to the outer side surface 102a of the stamped plate 100.
However, in the conventional heat exchanger, the joining portion 111 of the end plate 110 abuts against and brazed to the outer side surface 102a of the stamped plate 100 at a location corresponding to at least two recessed portions of the recess 102, as noted above. As a result, an enclosed space 130 is defined in the joined portions of the end plate 110 and the stamped plate 100. In addition, the joining portion 111 of the end plate 110 and the outer side surface 102a of the stamped plate 100 are joined together in a face-to-face manner by brazing so that usually gaps such as pinholes can be formed in the brazed surfaces.
As a consequence, when a refrigerant flows in a refrigerant passage formed between the recess 102 of the paired stamped plates 100 to cool ambient air surrounding the enclosed space 130, the resulting condensed moisture in the ambient air enters the enclosed space 130 through the gaps such as pinholes. As the temperature of the enclosed space 5 further lowers, the condensed moisture becomes frozen to be swelled, which can cause exfoliation of the brazed surfaces in the vicinity of the enclosed space 130.